A common prior art technique for coupling light from an external source to a silicon waveguide is to cleave or polish end facets on both the waveguide and the mating fiber termination. Examples of fiber terminations include, but are not limited to: multimode or single-mode fibers with small or zero cleave/polish angles, and specially-shaped or lensed single-mode fibers that produce spot sizes as small as 1.5 μm. The fiber termination is aligned to allow maximum light transmission through the waveguide, and then fixed in position. Anti-reflection (AR) coatings can be used on both the fiber termination and the waveguide facet to reduce the Fresnel losses. In all of these prior art arrangements, the input and output ports are necessarily located at edge facets of the waveguiding-containing wafer die, significant restrictions on device geometry (e.g., topology and/or size) are imposed by using this prior art edge coupling constraint.
Another factor associated with optical coupling is the development and use of extremely “thin” waveguides formed within the SOI layer of an SOI-based opto-electronic arrangement. For the purposes of the present invention, a “thin” waveguide is defined as having a typical width on the order of approximately 0.5 μm and a typical thickness on the order of approximately 0.15 μm. In the past, “nanotapers” or “inverse tapers” have been successfully used with thin waveguides. However, this success has been shown only within research/development environments, where there is careful control over fabrication conditions.
Thus, a need remains in the art for a manufacturable, high efficiency optical coupling arrangement for providing permanent coupling of lasers and fibers into thin, SOI-based optical waveguides as utilized will be required for high volume production of opto-electronic products.